Outside of Vixen there isn't much in the way of after purchase support for Asian mounts. Don Rothman and I keep some salvaged stuff around, by the HEQ-5/Sirius isn't a common junker. Some parts can be replaced with common hardware, but castings and main axis gearsets are hen's teeth.

Never seen a busted HEQ5 to get spares from in the UK except the odd one where the mount is in such bad shape it would be useless as a source for parts. Maybe thats a testament to the mounts durability.

The UK importer can get spare parts if you can wait. They got me a few bis some time ago for a rebuild, cosmetic items only though but I have no reason to doubt they could get some other bits if asked sweetly enough.

PS one of the nist I know they can get is spare motor control boards but they are very pricey, from hazy memory someone sometime ago in the UK got one after a blow out on the main board and it was circa £200 but thats a hazy memory.